Means for producing superheated vapor



' March 4, 1958 r w. ENGEL 2,825,314

MEANS FOR PRODUCING SUPERHEATED VAPOR M Filed Dec. 16, 1954 fiy q \MAAAAAMM vvvvvwvvvv INVENTOR. WIL TE/PE/YGEL United States PatentO" MEANS FOR PRODUCING SUPERHEATED VAPOR Walter Engel, Nenss (Rhine), Germany, assignor to Sulzer Freres, Societe Anonyme, Winterthur, Switzer--' The present invention relates to forced flow steam or vapor generators of the once-through type, in which the steam or vapor is generated at critical or supercritical pressure.

In forced flow steam or vapor generators in which the working medium is converted from the liquid phase to the vapor phase at critical or supercritical pressure, no boiling of the liquid occurs, and irregularities which are caused by boiling phenomena are avoided. When generating steam or vapor above the critical pressure, the feed water or liquid medium is subjected to a pressure which is at least equal to the critical pressure. If the liquid is heated at this pressure up to the critical temperature, the liquid is transformed into vapor without any clearly defined change of phase such as boiling when operating at subcritical pressures. If additional heat is supplied, the I vapor is immediately superheated.

In conventional forced flow generators in which vapor or steam is generated in this manner and in which heat is transmitted to the operating medium in a first part by radiation, and in a second part by contact of hot combustion gases with boiler tubes, the zone in which the liquid is converted into vapor is usually arranged in the combustion chamber. Here, however, the heat is transmitted by radiation and is too great, since only a relatively small amount of heat is necessary for converting a liquid into vapor at supercritical pressure. It has been proposed to place the conversion zone of the heating surface into the region in which the heating is effected by contact with the hot furnace gases, and to arrange the heating surface in which the vapor is superheated in the combus- 2,825,314 l atented Mar. 4, 1958 "ice cooling causes reconversion of all or part of the generated vapor into liquid, affording blowing down of liquid containing salts and impurities. Only the heat in the blown down liquid is lost, the heat transferred into the cooling liquid merely raising the temperature of the liquid which is fed into the generator.

In the heat exchanger in which the liquid is heated by superheated vapor and itself converted into vapor, the superheated heating vapor may be conducted inside the heating tubes and the liquid and vapor produced therefrom may be outside of the tubes, affording easy cleaning of the heat exchanger, since the only part of the steam generating apparatus according to the invention where scale may be formed is the conversion zone, i. e. the zone in which the liquid is transformed into vapor.

The tubes in the heat exchanger carrying the superheated heating vapor may be arranged within tubes of larger cross section which carry the liquid to be converted heat exchanger, the medium may be conducted outside of the heatexchanger into an indirect cooler through which liquid operating medium is conducted prior to being fed into a preheater which may be heated by combustion gases of the generator. The cooler may be arranged in parallel relation to the feed line for the generator, so that the portion of the liquid to be fed into the generator which passes through thecooler can be adjusted. In that case a valve is preferably provided at the inlet of the cooling liquid into the cooler, a second valve being provided in t the portion of the feed line by-passing the cooler, so that tion chamber. In this case, however, the superheater tubes Y which are exposed to radiation are subjected to high heat stresses which may cause difficulties.

These ditticulties are avoided by the present invention, according to which the liquid is heated by radiant heat to a temperature below the critical temperature and is converted into vapor by heat exchange with superheated vapor in a heat exchanger which is arranged outside of the flow of the combustion gases and which is not exposed to radiant heat. The vapor thus produced is superheated by radiant heat and/ or by heat transfer from combustion gases by convection and is used for heating the heat exchanger in which the liquid is converted into vapor. The heating vapor leaving the heat exchanger is once more superheated by the combustion of fuel and by heat transfer by radiation and/or convection.

According to the invention, a continuous stream of liquid operating medium is continuously converted into vapor and is immediately superheated to the desired temperature at which the vapor is used.

In a modification of the apparatus according to the invention, the operating medium which has received some heat from superheated vapor in the heat exchanger in which the liquid operating medium is converted into vapor, is cooled by indirect heat transfer to liquid opereither a part of the liquid operating medium, or all of it, can be passed through the cooler, or no liquid operating medium can be passed through the cooler prior to being fed into the generator.

With the system according to the invention, the working medium can be cooled and liquid containing salts and impurities can be blown down in desired amounts without interrupting the circulation of the working medium through the generator and without interrupting vapor generation.

The terms liquid and vapor used in the present specification and in the claims include water and steam. Where the words water and steam are used, these include substances in liquid and vapor state other than water and steam. The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself however and additional objects and advantages thereof will best be, understood from the following description of embodiments thereof when read in conjunction with the accompanying drawing, in which Fig. 1 is a diagrammatic illustration of a vapor generator according to the invention;

Fig. 2 is a diagrammatic illustration of a modified vapor generator according to the invention, comprising cooling means interposed in the conversion zone;

Fig. 3 illustrates a modified portion of the vapor generator shown in Fig. 1.

The same numerals designate the same parts in all figures.

In the forced flow once-through vapor generator shown in Fig. 1, the liquid working medium is fed, at least at the critical pressure of the medium, into a preheater 2 which is situated in a flue gas duct 1. From the preheater 2, the liquid flows into a heater 4 which is disposed in a combustion chamber 3, for receiving heat substantially by radiation. The liquid operating medium leaves the heater 4 at a temperature below the critical temperature of the medium. Thereupon the liquid passes anaemia .3 through a tube 6 disposed in a special heating chamber of a heat exchanger 5, in which the working medium is converted from the liquid into the vapor or gas phase.

If the working .medium is water,--it .may .ententhe .tube

6, fonexarnple "at 370 C., and leave. the ,tube.=6 iin.tlie. form ofsteamtof, :for example, 380" .C. This steam. flows into .a superheater 7. adapted .to. receive. heatisubstantially byradiationyin thechamberS. I The superheated steamjs conducted in counter-flow to thesmedium to vbe converted into-steam through the heating chamberr5'..for heatingtthetube 6. .T hereby .the superheated, steam loses apartzof. its ,heat .content, which is restored ..to.it.-.in..a superheaten: 8 arranged in the radiant t heat. chamber. The steam is further superheated in another. superheater 9 which receives heat bycontacttwith the combustion gases.

The tube. 6 in which the liquid is convertedinto vapor issituated outside of the radiant heat chamber 3 vandis alsooutof contact withthefit1e.gases,xthe tube. 6.being heateduindirectly by superheatedsteam from the-same system without being exposed to radiant. or convection heat resulting fromthe combustion of fuel.

In the vapor generator .shown in Fig. 2, the system of steam generation employed is similar to. that ofFig. 1. In addition, however, .thetube. 6 is provided with a section 10 of enlarged cross section which is not heated: by superheated steam. Themedium flowing through this enlarged section is,.cooled for reconversion into liquid form. towatford blowing down of liquid containingusalts through a blow-down pipe 11'. The cooling of the workingmediumw'hich is conducted. thronghtheenlarged tube section 10is effected by using liquid workingmcdium flowing-to the preheater 2 as a cooling agent. .This cooling liquid is taken from a feed pipe 12 and:is conducted into a .tube placed within the enlarged tubesec tion 10. by means ofan inlet pipe 13. The cooling liquid flows from :the-cooler 10 through an outlet pipe 14: and a connecting pipe 15 into the preheater 2. Valves 17 and 18 are provided, respectively, in the inletpipe 13 and in a pipe 16 by-passing the cooler 10.

If all of the liquid required for feeding the vapor generator is used as cooling medium, the valve. 17 is opened and the valve.18 is closed. If only some of the liquid is to be used as cooling agent for the cooler 10, the valves 17 and 18 are correspondingly adjusted and the liquid not requiredfor cooling flows directly throughthe bypass pipe 16 .into the connecting pipe 15. When .no blowing-down is needcd,..the valve 17 is .closed and the entire liquid stream flows through the bypass pipe 16 and through the connecting pipe :15 into the :preheater 2.

Instead of conducting the liquid to be converted into 4 vapor in the heat exchanger 5 inside of a tube 6 and passing the superheated vapor for heating the tube 6 outside of the latter, the superheated vapor may be conducted through a conduit 5" and the medium to be heated may be passed in counter-flow relation through a conduit 6' which surrounds...the..conduit 5". This is shown in Fig. 3.

While -'specific embOdiments of lthe invention .have

1 been shown and described,'"it will be apparent to those skilledin...the ..art....that various changes, modifications; substitutions, additionsiandomissions.may .be made .thercin without departing ifromzttheispirittandscopetof .the-invention as setforth in the appended claims.

What is claimed is:

1. An apparatus-,forproducing superheated vapor of at least critical pressure from a liquid operating medium comprising a furnace for burning fuel, a heating tube systemheatedby combustiongasfrom saidfurnace, means -.supenheated vapor...as heating agent therefrom anda superheater connected with said. heat exchanger for receiving.:.and. resuperheatingthe vapor which has served as heatingagentin. said. heat exchanger.

.l 2.. An. apparatusaccording to claim 1 including a feed pipe. forsaidheating .tube system, said cooler including a conduit .connected with .andby-passing a portion of said feed,.pipe..for conducting liquid operating medium as cooling agent through said cooler.

References Cited in the 'file of this patent UNITED, STATES PATENTS *1,784,426 Gleichrnann Dec. 9, 1930 2,035,908 Michel Mar. 31, l936 2,594,8'l8 .Sprague et al. Apr. 29, 1952 :FOREIGN. PATENTS "732,174 Germany Feb. 24, 1943 

